Mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have been identified in achondroplasia, hypochondroplasia, thanatophoric dysplasia and platyspondylic lethal skeletal dysplasia, San Diego type, four of the most common dwarfing conditions in humans. This work will define the role of FGFs in human chondro-osseous growth and provide an in vitro system for testing therapeutic approaches to achondroplasia.